1. Field of the Invention
The present invention relates to technique for correcting distortion in an image displayed on a projection screen by a projector.
2. Description of the Related Art
Projectors display images by modulating light from an illumination optical system in response to an image signal by means of a liquid crystal light valve, and projecting the modulated light onto a projection screen by means of a projection optical system.
When an image is projected and displayed onto the projection screen, if the center axis of the light representing the image (image light) emitted by the projector is not normal to the projection screen, the image on the projection screen experiences roughly trapezoidal distortion. Such distortion in a displayed image can be corrected by adjusting the image formed on the liquid crystal light valves.
However, to date it has been relatively difficult to correct distortion in an image displayed on a projection screen. This is because correcting distortion in a displayed image requires to know an angle between the center axis of the image light emitted by the projector and the normal of the projection screen, and knowing the correct angle is relatively difficult.
Specifically, the conventional process for adjusting the projection direction of a projector requires the user to manually adjust the height (extension) of the legs provided on the bottom of the projector. The angle of the center axis of the image light emitted by the projector with respect to the normal of the projection screen is determined according to the height of the legs. However, the process of adjusting the height of the projector legs is quite laborious.
In view of the drawbacks of the prior art described above, it is an object of the present invention to provide a technique for easily correcting distortion in an image displayed on a projection surface.
At least part of the above and the other related objects is attained by an apparatus which is a projector for displaying an image onto a projection surface. The projector comprises: a display image data generator for generating display image data representing a display image to be displayed on the projection surface by using source image data; an electro-optical device for emitting light that forms an image in response to the display image data; and a projection optical system for projecting light emitted by the electro-optical device. The projection optical system comprises a variable angle mirror for reflecting light emitted by the electro-optical device. The display image data generator comprises: an angle information sensing section for sensing angle information for the mirror; and an image data adjusting section for adjusting the source image data in response to the angle information so as to correct distortion of the display image displayed on the projection surface, to generate the display image data.
This projector comprises a variable angle mirror for reflecting light emitted by the electro-optical device, and an angle information sensing section for sensing angle information for the mirror, whereby it is a simple matter to determine the angle formed by the center axis of the image light emitted by the projector and the normal of the screen SC.
In the above apparatus, it is preferable that the mirror is rotatable about a predetermined center axis, and the angle information sensing section senses the angle information for the mirror centered on the predetermined center axis.
The angle information sensing section may comprise a rotary encoder, a moveable portion of the rotary encoder moving in association with rotation of the mirror.
By so doing, the angle information sensing section can readily sense angle information for the mirror. The rotary encoder may be of absolute type or incremental type.
Alternatively, the angle information sensing section may comprise a variable resistor, a moveable portion of the variable resistor moving in association with rotation of the mirror.
In this way as well the angle information sensing section can readily sense angle information for the mirror. The variable resistor may have three terminals (i.e. a potentiometer) or two terminals.
The above apparatus may further comprise a mirror controller for causing the mirror to rotate.
This obviates the need for the user to operate the mirror directly in order to adjust the angle thereof.
In the above apparatus, it is preferable that the display image data generator further comprises a distance information acquiring section for acquiring information about the distance between the projector and the projection surface; and the image data adjusting section generates the display image data according to the angle information and the distance information.
By so doing, distortion in a displayed image can be corrected precisely.
The distance information acquiring section may comprise a distance information sensing section for sensing the distance information.
By so doing, distance information can be determined easily.
In the above apparatus, the projection optical system may have a zoom function, and the distance information sensing section may sense the distance information using a zoom position of the projection optical system.
By so doing, information regarding the distance between the projector and the projection surface can be sensed precisely.
In the above apparatus, the mirror may be rotatable about two mutually orthogonal center axes, and the angle information sensing section may sense two sets of the angle information for the mirror centered on the two center axes.
While a displayed image can undergo roughly trapezoidal distortion in two directions, depending on the spatial relationship of the projector and the projection surface, image distortion occurring in two directions can be corrected by the above arrangement.
These and other objects, features, aspects, and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with the accompanying drawings.